817 



of cliromoiissnlphate ran into tube /. The porous 

 cup was removed and tube / was closed at the 

 top. The liquid was sucked off through the three- 

 waj-cock D, the crystals remained on the asbestos 

 filter in /. These crystals were washed with 

 oxygen-free water, and the washing water 

 sucked off throug-h D. Then the chromoussnlphate 

 was dissolved in water, and this solution con- 

 veyed to tube //, which was likewise fdled with 

 carbonic acid. From II this solution could be 

 conveyed into other vessels through /ƒ/, in which 

 carbonic acid was admitted through G, so that 

 also in this operation the chromous-sulphate was 

 only in contact with carbonic acid. 



In this way a pure blue solution of chromous- 

 sulphate was obtained. It was generally not free 

 from acid, because it is impossible to wash till 

 all the sulphuric acid has been expelled without 

 a great loss of chromous-sulphate. To remove the 

 free sulphuric acid, a small quantity of baryt 

 water was finally added. 



5. The chromium electrodes used. 



For the measurements of the potential three kinds of electrodes 

 were used. First small pieces of chromium according to Gold- 

 SCHMIDT, which were cemented into glass tubes, in which a drop 

 of mercury and a copper wire was brought. 



Secondly chromium, which had been deposited electrolytically 

 from a solution of 127o chromic-sulphate and 137o chromic acid ^) 

 on a copper wire of 3 mm. thickness. The current density amounted 

 to 80 Amp./dm'* at a velocity of revolution of the cathode of 800 

 Rev. /min. 



The amount of metal deposited by the current was only lö"/,, 

 of the theoretical. The metal was of a fine grey colour, and 

 adhered well to the electrode when the layer was not too thick; 

 otherwise there was a tendency to scale off. 



The third kind of chromium electrodes consisted of copper wire 

 which had been electrolytically chromated in a solution of chromic 

 chloride, which contained 100 gr. Cr. per L. *). Under the same 



^) FoERSTER, Elektrochemie wassriger Lösungen, Leipzig 1915, 491. 

 2) Garveth and Mott. Journ. f. phys. Chemistry 9, 231, (1905). 



